Intersol'2021 - Paris

Don't miss the presentation by our expert Chloé Milloz at the workshop on "Soil, an opportunity for urban development"

Thursday 9^th September 12h20 - Land reclamation and development with a temporary occupation of the urban area "Gratte-Ciel"  in Villeurbanne

Chloé Milloz, Environnement manager of SCE Lyon branch

Full programm  here

« Gratte Terre Project » : Experiment to revive urban soil

INTRODUCTION
In 2020, a temporary occupation initiative was launched in Villeurbanne center city. A selection of projects was granted an agreement for temporary occupation for part of the ZAC Gratte-Ciel, amongst which the “Gratte Terre” project.

“Gratte Terre” project is led by a consortium gathering following actors:

• SCE: urban planning and environment firm _ lead of the consortium
• Parc et Sport: landscaping company
• Thierry Boutonnier : Artist
• Jardins d’Yvonne: gardening association
• SPES : Academic support association

The temporary occupation is an opportunity to quickly and effectively experiment responses to environmental and social issues. “Gratte-Terre” project was designed to:

• Coordinate in-situ experiments on fertile soils reconstitution in a dense urban environment ;
• Develop a tree nursery based on local vegetal species encountered around the city center, to allow reusing them in the future urban development project ;
• Identify alternative solutions to excavation and export of urban soils, reusing them within the framework of a circular economy ;
• Provide a space for meeting, sharing and learning about environment, agriculture and food production in the city.

Main challenges for the project success are:

• Organize and pilot the temporary occupation, which brings together private and associative structures around nature in the city
• Capitalize, through the creation of technical and organizational references, to advocate for sustainable approaches in urban planning projects (soil reuse, fight against the « heat island » effect, .

EXPERIMENT
1. Fertile soil reconstitution
Urban soils are natural soils that have been disturbed by development in a way that affects their functioning and properties. In urban projects, excavated soils are often disposed of at landfills and the recycling rate for high quality purposes is low. Moreover, the wasteland is often let mineral and unused during many years, reinforcing the “heat island” effect.

The experiment aims at the reconquest and/or upgrading of urban soils onsite, involving their reuse in the future urban project. This reuse may replace totally or partially the usual substitution by fertile outdoor soils.

3 different natures of soils were experimented at the site:

• Fertile soils
• Mix of inert soils (excavated from neighboring urban projects) and compost
• Pure compost

Different types of seedlings were then used to experiment their effects on soil fertility restauration : Clover, moha, luppus, etc.

2. Creation of an urban nursery
The goal of this experiment is to impulse a circular plant economy within the future urban project of Gratte-Ciel, by providing plants that carry genetic and epigenetic adapted to the local context. It was declined in different steps:

• Collection of seeds considered as representative of the local urban biodiversity ;
• Experiment with different seeds savings and germination technics;
• Tree transplant

Both soil reconstitution and urban nursery will be studied from a technical and economic perspective over the 3 years planned for the project

More than an experiment, a collaborative project, seeking social, environmental and climatic impact

Beyond technical and economic aspects, the global impact of the temporary occupation for the suburb inhabitants is also key to our experimentation. As a matter of fact, the project also aims to:

• Reduce the heat island effect, through the development of vegetation on site
• Recycle green waste through the development of composters on site
• Educate the public on environmental issues: Gratte-Terre must become a place for sharing know-how, for education on ecology and a place for urban agriculture, hosting trainings for schools and associations for instance.